Pull my Finger has 18 different sounds while iFart Mobile has the "Sneak Attack" and the "Security Fart" functions, both of which are highly usefull.
About the sound effects I can safely say that Air-O-Matic (the developers of Pull my Finger) have really outdone themselves trying to recreate realistic sounding...
Wait! You can't possibly be serious about this!
It's a frickin fart app, dude!